(2) A positive MRZ reaction might be less frequent in children; while this might be due to the difference between prepubertal and postpubertal prevalence rates for rubella virus antibodies [8, 25], it may partly also reflect accidental inclusion of children with MOG-EM—a condition that is common among children with CNS demyelination (and even more common than MS in young children)—in previous pediatric studies. Here, MOG is linked to myeloid sarcoma.